This invention relates to a type cassette and, more particularly, to methods for manufacturing an audio tape cassette with an independent or separate, plastic molded, tape guide having integrated rollers for improving tape movement across the magnetic head of a tape player/recorder.
Separate, plastic molded, tape guides for tape cassettes are known in the art, as described most recently in co-owned U.S. Pat. No. 4,506,846 (now U.S. Re. Ser. No. 823,481), and shown in FIGS. 1 and 2 herein. More particularly, the tape cassette shown is indicated generally by reference numeral 10 and includes a bottom half 12 and a top half 14, preferably made of, but not limited to, a clear material. When assembled, the tape cassette 10 (and accordingly each cassette half 12 and 14) has, viewing from the bottom of FIG. 1, a front 16, a back 18, a left side 20 and a right side 22. Positioned within the tape cassette 10 are a first tape reel 24 and a second tape reel 26 which rotate to move tape 28 across the front 16 of the tape cassette 10.
Formed on the bottom half 12 of the tape cassette 10 are corner tape guiding shafts 30 and 32. There are also provided tape rollers 34 and 36 having through holes formed therein which are rotatably received by roller axial columns 38 and 40. The columns 38 and 40 are formed on bottom bosses 200, which together are molded as part of the bottom half 12. Corresponding top bosses 201 are formed on the top half 14 to receive the free ends of the columns 38 and 40 when the tape cassette 10 is assembled. The rollers 34 and 36 are located within areas defined by circular recesses 41 formed in both the top half 14 and bottom half 12, concentric to the bosses 200 and 201. As is the predominant practice in the industry, the rollers 34 and 36 are completely independent of the tape guide subassembly 44 which is located at the front 16 of the tape cassette 10 and which constitutes the conventional central tape support area.
As best seen in FIG. 2, to assemble the tape cassette 10, the columns 38 and 40 projecting from the empty bottom half 12 are lubricated and then the separate rollers 34 and 36 are positioned on the columns 38 and 40. The rollers 34 and 36 must thereafter be contained during the assembly process to prevent them from being dislocated as the bottom half 12 is transported to the tape guide subassembly station. The tape guide subassembly 44 is then positioned within a recess 42 formed in the bottom half 12 (the top half 14 has a complementary recess 46 formed therein) and the tape reels 24 and 26 with tape 28 extending therebetween are positioned on a substantially flat washer 54 having holes 50 formed therein located on the bottom half 12. The reels 24 and 26 are located by a pair of raised annular rings 21 formed on the bottom half 12. The tape 28 extends (from left to right) across the tape guiding shaft 30, the roller 34, the front of the tape guide subassembly 44, the roller 36 and the tape guiding shaft 32. A complementary washer 52 with holes 48 formed therein is then placed into the empty top half 14, which is then located on the bottom half 12. As a result, the free ends of columns 38 and 40 are received by recesses in bosses 201, and the reels 24 and 26 are also located by a pair of raised annular rings 23 formed on the top half 14 between the relatively central planar areas of the top and bottom halves, 14 and 12, respectively. The rollers 34 and 36 are then allowed to rotate during operation on the columns 38 and 40, respectively, while abutting bosses 200 and 201.
The conventional tape guide subassembly 44 described above provides some control over alignment of the tape 28 at the central tape support area in front of the tape guide subassembly 44 where the magnetic head makes contact with the tape 28 during operation. However, another important consideration in controlling tape alignment is the relationship of the rollers 34 and 36 to the tape guide subassembly 44.
When the columns 38, 40 are molded on the bottom half 12 and bosses 200, 201 are molded in both halves 12 and 14, molding imperfections can be expected. If the rollers 34 and 36 are then positioned on defective columns 38, 40, respectively, and abut defective bosses 200 and 201, tape misalignment can result between the top half 14 and the bottom half 12. Even the smallest misalignment can diminish tape recording/reproducing quality.
Another important drawback of the conventional use of rollers 34, 36 mounted on columns 38, 40 formed on the bottom half 12 is the inherent molding difficulties in creating accurate "concentricity" of the roller's inside diameter to its tape bearing surface. Attempting to create such concentricity requires careful and difficult control of very subtle parameters which, of course, increases the overall cost of manufacturing the tape cassette.
Further, due to various molding tolerances and assembly effects, a clearance is required axially of the roller 34, 36, i.e., between each end of the roller and the respective cassette halves 12 and 14. Although necessary, excessive clearance does not contribute to optimum tape recording/reproducing quality.
Finally, this tape cassette 10, like any tape cassette employing separate rollers between the cassette halves, exhibits the persistent drawbacks of misplacement of the rollers 34, 36, breakage of the columns 38, 40 and excess lubrication during assembly, each of which causes the tape cassette 10 to be scrapped during quality inspection.
On the other hand, the earlier U.S. Pat. No. 4,079,499, issued to BAGOZZI, discloses a tape cassette having a separately formed, metal tape guide incorporating rollers at the ends thereof as shown in FIG. 3 herein (BAGOZZI also briefly suggests a plastic molded tape guide with rounded ends, but generally teaches away from the use of plastic for tape cassette members, see Col. 3, line 1 and Col. 4, lines 37-63) More particularly, a tape cassette 58 is shown including a metal top half 60, a metal bottom half 62 and a metal tape guide 64 positioned therebetween. The metal tape guide 64 is made by repeatedly bending and blanking sheet metal to form front support surfaces 66 for the tape (not shown) and side supports 68 for receiving tape guide rollers 70. The tape guide 64 also has upper ears 72 and lower ears (not shown), allowing removable assembly between the halves 60 and 62 during assembly of the tape cassette 58. There is also provided lightening notches 76, which define therebetween tabs 78 bearing the side supports 68, such that the side supports 68 are elastic in a direction toward the back of the tape guide 64.
This tape cassette 58 is not known to have gained acceptance in the industry for the following reasons.
First, this metal tape guide 64 is believed to result in poor tape reproducing and recording quality because the rough metal front support surfaces 66 necessarily create unwanted friction with the travelling tape. It is, however, not believed to be practical to attempt to polish them enough to minimize friction.
Second, as is easily comprehended by viewing FIG. 3 herein, this metal tape guide 64 is made by a relatively complicated, time-consuming, costly, multi-step method, wherein the sheet metal must repeatedly be bent and blanked. Such bending and blanking does not easily lend itself to automation or adequate dimensional reproducibility for mass production purposes. For example, it would be very difficult to guarantee that each left side of the BAGOZZI tape guide could repeatedly be formed to the same exacting dimensions as the right side of the tape guide, a requirement for accurate tape tracking.
Third, metals are known to have certain imperfections or impurities therein which would affect the ability to accurately bend and blank the tape guide 64.
Fourth, any member in a tape cassette which can be magnetized, such as this metal tape guide 64, could quickly put an end to the useful life of the tape cassette.
Fifth, it appears from BAGOZZI (FIG. 3 therein) that a separate axial pin 69, presumably also made of metal, is provided for each of the rollers, with the pin 69 extending into through holes formed in the tape rollers and then through the side supports. Although not described, it appears clear that, in order to assemble the metal tape guide of BAGOZZI, external force must be used to separate each side support 68 to allow insertion of each roller 70. Then the through hole formed axially in each roller 70 must be visually lined up with the pair of colinear holes formed in the side support 68 before the pin 69 can be inserted from above or below, because there is no means for automatically directing the centerline of the roller 70 to the desired position. Once the pins 69 are inserted into the rollers 70, the pins 69 would have to be swedged or the tape guide would have to be quickly inserted into the cassette base 62 to prevent the pins 69 from falling out. Again, as with U.S. Pat. No. 4,506,846, discussed above, concentricity problems arise and a clearance must be provided between the rollers 70 and the side supports 68 for the rollers to rotate.
Sixth, in some manner each roller must be lubricated to facilitate rotation within the metal side supports. For example, the roller ends may be lubricated prior to insertion into the side supports. Instead, or in addition, the pins 69 may be lubricated prior to insertion into the rollers 70. In either case, once lubricated the rollers and/or pins would be difficult to handle. As a result, this method further increases assembly cost and complexity and thus does not lend itself to mass production of tape cassettes.
Seventh, and most importantly, although it is not clear from a review of BAGOZZI, it would appear that a clearance must also exist between the side supports 68 and the cassette halves 60 and 62, or else the pins 69 extending from the rollers 70 would contact the cassette halves 60 and 62 and impede rotation of the rollers 70 (see FIG. 8 of BAGOZZI). As a result, the side supports 68 intentionally remain elastic in the direction of the back of the tape cassette 58 during operation. Apparently, the side supports 68 are intended to act as shock absorbers to minimize tape slack during loading of the tape or during normal operation. Unfortunately, this shock absorber effect creates an ever-changing tape guiding surface, not a fixed, accurate surface which is preferred. Further, such a variable tape guide undoubtedly will vary the tape speed, resulting in wow and flutter, which is also a major disadvantage. Finally, it is also to be expected that the spring-like ability of the metal side supports 68 will diminish with time, adding to the ever-changing tape guiding surface.
Japanese Reference No. 56-50354 appears to show a plastic-molded, independent tape guide having rollers mounted for rotation at the ends thereof. It is not clear from this reference whether the rollers include a separate inserted or integrally formed axle. However, the tape guide taught by this reference suffers at least from the seventh drawback discussed above relative to BAGOZZI, and perhaps the fifth and sixth drawbacks also.
That is, the roller bearings which receive the rollers shown in the Japanese Reference are intentionally designed to flex elastically in a direction toward the back of the tape cassette during operation. As with BAGOZZI's tape guide, such a tape guide creates an ever-changing tape guiding surface, not the fixed accurate surface preferred.
In light of the above, methods for easier and less expensive manufacture of a tape cassette, including a separate tape guide characterized by improved tape alignment accuracy, is desired.